According to certain tire-building methods, tire manufacture can be broken down into two distinct steps. In a first step, the components comprising the carcass reinforcing ply and the bead reinforcing rings is built up on a drum, generally a cylindrical drum, to obtain a substantially cylindrical assembly often given the name carcass by extension of the name of one of its key components.
In a second step, the carcass is given a substantially toroidal shape and the components that form the crown reinforcing belt, notably including the crown reinforcing plies and the tread, are added.
These two operations are performed in different tire-building machines, and so it has been necessary to develop transfer means that allow the carcasses to be stored and moved around from the carcass-building machine to the crown-building machine.
These various means comprise, amongst other things, roller conveyors of the type like the one described in publication EP 659 542, on which the carcasses are place and stored while they are waiting to be taken up by the crown-building machine.
As a general rule, and to avoid deformation connected with the low rigidity of the carcass reinforcing ply, the carcasses are placed on the said conveyors in such a way that their axis is positioned horizontally, and perpendicular to the direction in which the carcass travels on the roller conveyor. The carcasses therefore rest directly on one of their generatrices.
However, when they are placed in this position, the carcasses experience deformation connected firstly with the effects of gravity.
One known solution, as described in publication WO 02/1822, is therefore to have the said carcasses rotating about their axis of revolution so that the effects of gravity are applied uniformly to all points on the circumference of the carcass.
To do that, the rollers of the conveyor are driven in rotation about their axis of rotation and are capable of translational movement in the direction in which the carcasses travel, which direction is perpendicular to the said axis of rotation of the rollers. These two movements of rotation and of translation of the rollers can be controlled independently of one another.
However, it is found that, while the carcasses are revolving on the roller conveyor, the carcasses deviate from their path in an axial direction (perpendicular to the direction of travel) because of slight geometric variations affecting their cylindrical overall shape. This then causes undesirable contact between the carcasses and one of the edges of the conveyor or between carcasses themselves, when they are positioned in line abreast across a wide conveyor. These contacts are likely to cause deformation to the unvulcanized elastomers of which the tire carcass in the process of being manufactured is made.
More generally, the problem as set out hereinabove also arises in respect of any device comprising at least one pair of rollers intended to support a tire carcass and in which the said rollers are set in rotation such that the carcass rotates about its axis in order not to experience deformations connected with the action of gravity.